Solar photovoltaic cells are semiconductor devices which produce a voltage across output terminals when exposed to sunlight, and typically a plurality of solar cells are interconnected in series to produce a desired voltage. In order to increase the electrical output, attention has been directed to the use of solar cells which operate under conditions of high intensity solar radiation, such as, for example, under conditions of solar fluxes up to hundreds of suns. Solar radiation at high intensities, such as 10-50 watts/cm.sup.2, can be achieved by the use of various light concentrating devices such as, for example, concentrating reflectors or lenses such as Fresnel lenses. As the solar radiation incident on a solar cell becomes more intense, the electrical output of the cell is increased; however, for efficient operation, the cell must remain cool in the presence of high radiation levels and therefore a good thermal link between the cell and the external environment is required. The thermal path must also be electrically insulating, and a breakdown voltage of at least about 2,000 volts is desired for some applications. Prior attempts to provide a barrier between solar cells and a heat sink in which the barrier has excellent dielectric strength and also provides adequate heat transmission, have only been partially successful. For example, thin Al.sub.2 O.sub.3 films which are anodically formed on an aluminum substrate exhibit excellent thermal conductivity, i.e., about 10 watts/meter-.degree.Kelvin; however, a portion of the surface is represented by micron-sized pores which severely limit dielectric breakdown strength to less than 1,000 volts. Electrophoretically-deposited styrene-acrylate films have also been tested as barriers. These films, in a thickness of about 40 microns, have dielectric strengths over 2,500 volts, but their thermal conductivity of 0.1 to 0.2 watts/meter-.degree.Kelvin is only marginally useful.